Faculty Member: Dr. Roberto Leon
EARTHQUAKE ENGINEERING- conducting computational simulations and experiments to better understand seismic behavior and improve design provisions for steel and composite structural systems.
Composite Structural Systems
Composite steel-concrete structures offer significant benefits in terms of strength, stiffness and ductility for design in seismic areas. This form of construction is popular in Japan, China, and the rest of Southeast Asia for tall buildings, and is recognized by USA codes. However, it is not commonly used because of the perceived lack of design provisions, particularly with respect to connections.
Specific research experimental topics include:
- Shear transfer between steel and concrete under large cyclic deformation reversals.
- Effect of composite diaphragm action, including:
- the appropriate values of stiffness and strength to be used in analysis,
- the presence of openings in the floor slab, any preexisting slab cracking, and the modeling of connections to chord and collectors,the interactions between in-plane and out-of-plane forces at the local level, and
- the degree of ductility and load path redundancy that can be obtained from diaphragms and their connections.
- Behavior and design of circular and rectangular concrete-filled tube columns with high strength concrete and slender tube sections under large cyclic load reversals.
- Behavior and design of composite connections between composite steel-concrete beams and concrete filled tubes with emphasis on local force transfer between steel and concrete.
- Shear and bearing force transfer between steel and concrete under large cyclic deformation reversals.
- Local buckling of composite sections.
- Plastic hinge length and rotational capacity.
- Advanced analytical models of connection behavior and performance, including combinations of shape-memory alloys and similar advanced materials to re-center connections and improve energy dissipation capacity.
- Incremental dynamic analysis of archetypes structures in support of development of structural system factors (R, Cd,and W0).
In conventional seismic systems, the primary lateral resisting structural elements deform inelastically to dissipate energy during a large seismic event. This inelastic deformation, a direct consequence of the use of ductility concepts in design, often leads to a large residual interstory drift, severe damage to structural and nonstructural elements, costly repairs, and large indirect economic losses after a major earthquake. The main thrust of this research is the development of a brace in which (1) the need for energy dissipation does not lead to residual deformations, and (2) the reuse of the re-centering component and easy replacement of the energy dissipating components damaged in an event are easily achievable. This device uses conventional buckling restrained struts to dissipate energy and superelastic shape memory alloy (SMA) wires to recenter the structure. These innovative robust hybrid braces considerably reduce permanent drift and are assembled from easily replaceable damageable elements – (Joint work with Drs. Walter Yang and Reginald Desroches – Georgia Tech)
Reinforced Concrete Beam-Column Joints
Evaluation of older reinforced concrete frames has focused on weaknesses related primarily to shear capacity of beams and columns as well as insufficient anchorage of reinforcement. In general little has been done to model large levels of joint shear strength and deformation for older frames where joint shear failure and pullout of the bottom bars is a possibility. Analytical studies are underway to develop an OpenSEES joint model capable of tracking this type of phenomenon.
Retrofit of Older Reinforced Concrete Moment Frames
This experimental work is will evaluate the efficacy of a new class of innovative systems with recentering and/or high damping capabilities, and will develop a framework for their design and implementation to retrofit reinforced concrete (RC) buildings. Five retrofit measures will be investigated to achieve this goal, consisting of novel bracing systems, beam-column connection elements, or columns wraps. Common advantageous characteristics of the systems include the ease of application (requiring little-to-no heavy machinery), scalability and adaptability, passive nature, and need for little-to-no maintenance through the life-cycle. Tests will be carried out on unretroffitted and retrofitted slices of a building using a large shaker (Joint work with Drs. Yang Wang and Reginald DesRoches – Georgia Tech)
Modern Sensors for Crack Detection in Steel Bridges
A wireless strain sensing system is under development to exploit the operation principle of a passive (batteryless) radio frequency identification (RFID) system. The system consists of an RFID reader and an RFID tag, where the tag includes an antenna and an integrated circuit (IC) chip. The reader emits interrogation electromagnetic signal to the tag (at power level P1), so that the tag is activated and reflects signal back to the reader (with power level P1′). This reflection is also called backscattering. The system is classified as passive because the RFID tag does not require its own power supply, i.e. the tag receives its operation power entirely through the electromagnetic emission from the reader (Joint work with Drs. Yang Wang and Manos Tentzeris – Georgia Tech).
Field Testing of Structures and Post-Earthquake Performance Assessment
Full-scale testing of structures and assessment of their service performance throughout their life cycle is an integral part of the code improvement process. This work is important for curved and skewed bridges and buildings with irregularities in strength and stiffness. Only high quality field data should be used to calibrate and validate models that can then be used for larger parametric studies.
Similarly, post-earthquake investigations, particularly those aimed at comparing levels of performance between different detailing approaches, are an important tool to assess the real strength and deformation capacity of structural systems. Work in this area in countries with construction practices similar to the USA (Chile and New Zealand, for example) is particularly valuable